Bottom Line:
Ion transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems.EnPEn can robustly capture ion transport in sub-millimeter architectures with submicron polyelectrolyte layers.We proof the strength of EnPEn for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.

ABSTRACTIon transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems. We report a new direct numerical simulation model coined EnPEn: it allows to solve a set of first principle equations to predict for multiple ions their concentration and electrical potential profiles in electro-chemically complex architectures of n layered electrolytes E and n polyelectrolytes PE. EnPEn can robustly capture ion transport in sub-millimeter architectures with submicron polyelectrolyte layers. We proof the strength of EnPEn for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.

f3: a) Selectivity of Sodium over Calcium as a function of numbers of layers b) Concentration profiles of ions in a two-bilayer assembly.

Mentions:
Figure 3a shows simulation results of a CEM modified with two bilayers, where one bilayer comprises one cPE and one aPE. Sodium selectivity generally increases with increasing number of layers. Experimental data of White et al.27 is in agreement with these simulations, the experimental data reported by Abdu et al.25 only partly agree with the model. Discrepancies arise in the observed decrease of selectivity for added cPE layers. While the simulation predicts no or only slight selectivity difference, the experimental data suggests a considerable decrease. With the EnPEn simulations at hand and the new supporting data by White et al.27, we now hypothesize that the deposition of an additional aPE layer reduces the integrity of the underlying cationic layer. Defects in this layer will spoil the mechanism of Donnan exclusion, effectively decreasing overall selectivity towards monovalent cations. Depositing more alternating layers of cation and anion exchange slowly pushes selectivity to an overall monovalent ion selectivity. If one would succeed to prepare stable fixed aPE layers, equally good selectivities or even better experimental results can be achieved using one layer with defined thickness and high charge density.

f3: a) Selectivity of Sodium over Calcium as a function of numbers of layers b) Concentration profiles of ions in a two-bilayer assembly.

Mentions:
Figure 3a shows simulation results of a CEM modified with two bilayers, where one bilayer comprises one cPE and one aPE. Sodium selectivity generally increases with increasing number of layers. Experimental data of White et al.27 is in agreement with these simulations, the experimental data reported by Abdu et al.25 only partly agree with the model. Discrepancies arise in the observed decrease of selectivity for added cPE layers. While the simulation predicts no or only slight selectivity difference, the experimental data suggests a considerable decrease. With the EnPEn simulations at hand and the new supporting data by White et al.27, we now hypothesize that the deposition of an additional aPE layer reduces the integrity of the underlying cationic layer. Defects in this layer will spoil the mechanism of Donnan exclusion, effectively decreasing overall selectivity towards monovalent cations. Depositing more alternating layers of cation and anion exchange slowly pushes selectivity to an overall monovalent ion selectivity. If one would succeed to prepare stable fixed aPE layers, equally good selectivities or even better experimental results can be achieved using one layer with defined thickness and high charge density.

Bottom Line:
Ion transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems.EnPEn can robustly capture ion transport in sub-millimeter architectures with submicron polyelectrolyte layers.We proof the strength of EnPEn for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.

ABSTRACTIon transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems. We report a new direct numerical simulation model coined EnPEn: it allows to solve a set of first principle equations to predict for multiple ions their concentration and electrical potential profiles in electro-chemically complex architectures of n layered electrolytes E and n polyelectrolytes PE. EnPEn can robustly capture ion transport in sub-millimeter architectures with submicron polyelectrolyte layers. We proof the strength of EnPEn for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.